(a) Field of the Invention
The present invention relates to thin film transistors for liquid crystal displays.
(b) Description of the Related Art
Recently, liquid crystal displays (LCDs) using amorphous silicon thin film transistors (hereinafter “TFTs”) as switching elements are widely used in notebook personal computers and car navigation systems.
However, photo leakage currents due to the light incident on the amorphous silicon are generated in the thin film transistors, which deteriorate the characteristics of the liquid crystal displays.
A thin film transistor to reduce the photo leakage current is disclosed in U.S. Pat. No. 4,990,981 (Tanaka et al.).
However, the photo leakage currents generated in the amorphous silicon layer may not be considerably reduced in the TFT of Tanaka et al., since the amorphous silicon layer is not completely shielded by the gate electrode from the incident light from the lower side of the substrate.
Furthermore, the gate electrodes and the source/drain electrodes of Tanaka et al. may be easily shorted, since portions of the gate electrodes and the source/drain electrodes overlap via only a single insulating layer. In particular, the insulating layer may be open near the edge of the gate electrode, thereby causing the short between the gate electrodes and the source/drain electrodes.
In the meantime, because the kick-back voltage due to the parasitic capacitances between the gate electrodes and the drain electrodes cause flicker and afterimage etc., it is necessary to reduce the parasitic capacitance.